Detection and estimation of radio frequency variations

ABSTRACT

A system including a counting module, a difference module, and a radar module. The counting module counts polarity reversals of samples of a signal. The samples are generated during a first period, a second period, and a third period. The counting module generates a first count, a second count, and a third count of the polarity reversals counted during the respective periods. The difference module determines a first difference between the first count and the second count, a second difference between the second count and the third count, and a third difference between the first difference and the second difference. The radar module determines variation in frequency of the signal based on the first count and the second count, and determines a type of radar present in the signal based on one or more of the third difference and the variation in the frequency of the signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/825,775, filed on Jun. 29, 2010, which is a continuation ofU.S. patent application Ser. No. 11/493,473 (now U.S. Pat. No.7,747,222), filed on Jul. 26, 2006, which claims the benefit of U.S.Provisional Application No. 60/749,222, filed on Dec. 9, 2005. Theentire disclosures of the above applications are incorporated herein byreference.

FIELD

The present disclosure relates to wireless networks, and moreparticularly to a system and method for detecting and measuringfrequency variations in wireless signals.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

The I.E.E.E. has defined several different standards for configuringwireless networks and devices. For example, 802.11, 802.11(a),802.11(b), 802.11(g), 802.11(h), 802.11(n), 802.16, and 802.20.According to these standards, wireless network devices may be operatedin either an infrastructure mode or an ad-hoc mode.

In the infrastructure mode, the wireless network devices or clientstations communicate with each other through an access point. In thead-hoc mode, the wireless network devices communicate directly with eachother and do not employ an access point. The term client station ormobile station may not necessarily mean that a wireless network deviceis actually mobile. For example, a desktop computer that is not mobilemay incorporate a wireless network device and operate as a mobilestation or client station.

Referring now to FIG. 1, a first wireless network 10 is illustrated inan infrastructure mode. The first wireless network 10 includes one ormore client stations 12 and one or more access points (AP) 14. Theclient station 12 and the AP 14 transmit and receive wireless signals16. The AP 14 is a node in a network 18. The network 18 may be a localarea network (LAN), a wide area network (WAN), or another networkconfiguration. The network 18 may include other nodes such as a server20 and may be connected to a distributed communications system 22 suchas the Internet.

Referring now to FIG. 2, a second wireless network 24 operates in anad-hoc mode. The second wireless network 24 includes multiple clientstations 26-1, 26-2, and 26-3 that transmit and receive wireless signals28. The client stations 26-1, 26-2, and 26-3 collectively form a LAN andcommunicate directly with each other. The client stations 26-1, 26-2,and 26-3 are not necessarily connected to another network.

To minimize radio frequency (RF) interference, some wireless networksmay operate in a 5 GHz band. However, regulatory requirements governingthe use of the 5 GHz band vary from country to country. Some countriesutilize the 5 GHz band for military radar communications. Therefore,wireless networks operating in the 5 GHz band generally employ dynamicfrequency selection (DFS) to avoid interference with radarcommunications. A network device generally employs DFS to a differentchannel of the 5 GHz band to avoid interfering with radarcommunications.

In infrastructure mode, the AP 14 transmits beacons to inform the clientstations 12 that the AP uses DFS. When the client stations 12 detectradar on a channel, the client stations 12 notify the AP 14. Based onthis information, the AP 14 uses DFS to select the best channel fornetwork communications that will not interfere with radar.

In ad-hoc mode, one client station may be designated as a DFS owner. TheDFS owner is responsible for collecting reports from the other clientstations. If any station in the ad-hoc network detects radar, the DFSowner uses DFS to select the best channel for network communicationsthat does not interfere with radar. For example, if station 26-1 is theDFS owner, it will be responsible for collecting reports from stations26-2 and 26-3. If any station 26-1, 26-2, and 26-3 detects radar,station 26-1 will used DFS to select the best channel and notifystations 26-2 and 26-3 to switch to that channel.

SUMMARY

A system comprises a sampling module, a counter module, and a frequencycharacteristic module. The sampling module samples radio frequency (RF)signals on a first channel for a first predetermined period and a secondpredetermined period that is subsequent to the first predeterminedperiod. The counter module increments first and second counts when thesamples collected during the first and second predetermined periodsreverse polarity, respectively. The frequency characteristic moduledetermines a frequency of the RF signal based on at least one of thefirst and the second counts and determines frequency variation of the RFsignal based on the first and second counts. At least one of the firstand second counts is equal to the frequency.

In another feature, the frequency characteristic module compares thefirst and second counts to determine the frequency variation. Thefrequency characteristic module determines that the RF signal is toneradar when the first and second counts are approximately equal.

In another feature, the sampling module samples the RF signals for athird predetermined period that is subsequent to the secondpredetermined period and wherein the counter module increments a thirdcount when the samples collected during the third predetermined periodreverse polarity.

In another feature, the system further comprises a derivative modulethat determines a first difference between the first and second countsand a second difference between the second and third counts. Thederivative module determines a third difference between the first andsecond differences. The derivative module determines the first andsecond differences when the first, second, and third counts are greaterthan a predetermined threshold.

In another feature, the frequency characteristic module determines thatthe RF signal is chirp radar when the third difference is less than apredetermined threshold. The predetermined threshold is approximatelyzero.

In another feature, the frequency characteristic module determines thatthe RF signal is chirp radar when the third difference is approximatelyzero.

In another feature, the system further comprises a radar module thatdetermines whether the RF signal is one of chirp radar and tone radarbased on the frequency variation. The radar module determines that theRF signal is chirp radar when the frequency variation is linear. Theradar module determines that the RF signal is tone radar when thefrequency variation is approximately zero.

In another feature, the system further comprises a dynamic frequencyselection (DFS) module that communicates with the radar module and thatselects a second channel having a different frequency than the firstchannel when the radar module determines that the RF signal is one ofchirp radar and tone radar.

In another feature, at least one of the samples is disregarded andexcluded from the first and second counts when an absolute value of theat least one of the samples is less than a predetermined threshold.

In another feature, the predetermined threshold is approximately 0.1.

In another feature, the first and second periods are adjacent.

In another feature, the first, second, and third periods are adjacent.

In another feature, a wireless network device comprises the system.

In another feature, a radar detection device comprises the system.

In still other features, a method comprises sampling radio frequency(RF) signals on a first channel for a first predetermined period and asecond predetermined period that is subsequent to the firstpredetermined period, incrementing first and second counts when thesamples collected during the first and second predetermined periodsreverse polarity, respectively, determining a frequency of the RF signalbased on at least one of the first and the second counts, anddetermining frequency variation of the RF signal based on the first andsecond counts. At least one of the first and second counts is equal tothe frequency.

In another feature, the method further comprises comparing the first andsecond counts to determine the frequency variation. The method furthercomprises determining that the RF signal is tone radar when the firstand second counts are approximately equal.

In another feature, the method further comprises sampling the RF signalsfor a third predetermined period that is subsequent to the secondpredetermined period and incrementing a third count when the samplescollected during the third predetermined period reverse polarity.

In another feature, the method further comprises determining a firstdifference between the first and second counts and a second differencebetween the second and third counts. The method further comprisesdetermining a third difference between the first and second differences.

In another feature, the method further comprises determining the firstand second differences when the first, second, and third counts aregreater than a predetermined threshold.

In another feature, the method further comprises determining that the RFsignal is chirp radar when the third difference is less than apredetermined threshold. The predetermined threshold is approximatelyzero.

In another feature, the method further comprises determining that the RFsignal is chirp radar when the third difference is approximately zero.

In another feature, the method further comprises determining whether theRF signal is one of chirp radar and tone radar based on the frequencyvariation. The method further comprises determining that the RF signalis chirp radar when the frequency variation is linear. The methodfurther comprises determining that the RF signal is tone radar when thefrequency variation is approximately zero.

In another feature, the method further comprises selecting a secondchannel having a different frequency than the first channel when the RFsignal is one of chirp radar and tone radar.

In another feature, the method further comprises disregarding andexcluding at least one of the samples from the first and second countswhen an absolute value of the at least one of the samples is less than apredetermined threshold.

In another feature, the predetermined threshold is approximately 0.1.

In another feature, the first and second periods are adjacent.

In another feature, the first, second, and third periods are adjacent.

In still other features, a system comprises sampling means for samplingradio frequency (RF) signals on a first channel for a firstpredetermined period and a second predetermined period that issubsequent to the first predetermined period. The system comprisescounter means for incrementing first and second counts when the samplescollected during the first and second predetermined periods reversepolarity, respectively. The system further comprises frequencycharacteristic means for determining a frequency of the RF signal basedon at least one of the first and the second counts and determiningfrequency variation of the RF signal based on the first and secondcounts. At least one of the first and second counts is equal to thefrequency.

In another feature, the frequency characteristic means compares thefirst and second counts to determine the frequency variation. Thefrequency characteristic means determines that the RF signal is toneradar when the first and second counts are approximately equal.

In another feature, the sampling means samples the RF signals for athird predetermined period that is subsequent to the secondpredetermined period and wherein the counter means increments a thirdcount when the samples collected during the third predetermined periodreverse polarity.

In another feature, the system further comprises derivative means fordetermining a first difference between the first and second counts and asecond difference between the second and third counts. The derivativemeans determines a third difference between the first and seconddifferences. The derivative means determines the first and seconddifferences when the first, second, and third counts are greater than apredetermined threshold.

In another feature, the frequency characteristic means determines thatthe RF signal is chirp radar when the third difference is less than apredetermined threshold. The predetermined threshold is approximatelyzero.

In another feature, the frequency characteristic means determines thatthe RF signal is chirp radar when the third difference is approximatelyzero.

In another feature, the system further comprises radar means fordetermines whether the RF signal is one of chirp radar and tone radarbased on the frequency variation. The radar means determines that the RFsignal is chirp radar when the frequency variation is linear. The radarmeans determines that the RF signal is tone radar when the frequencyvariation is approximately zero.

In another feature, the system further comprises dynamic frequencyselection (DFS) means for communicates with the radar means andselecting a second channel having a different frequency than the firstchannel when the radar means determines that the RF signal is one ofchirp radar and tone radar.

In another feature, at least one of the samples is disregarded andexcluded from the first and second counts when an absolute value of theat least one of the samples is less than a predetermined threshold.

In another feature, the predetermined threshold is approximately 0.1.

In another feature, the first and second periods are adjacent.

In another feature, the first, second, and third periods are adjacent.

In another feature, a wireless network device comprises the system.

In another feature, a radar detection device comprises the system.

In still other features, a computer program executed by a processorcomprises sampling radio frequency (RF) signals on a first channel for afirst predetermined period and a second predetermined period that issubsequent to the first predetermined period, incrementing first andsecond counts when the samples collected during the first and secondpredetermined periods reverse polarity, respectively, determining afrequency of the RF signal based on at least one of the first and thesecond counts, and determining frequency variation of the RF signalbased on the first and second counts. At least one of the first andsecond counts is equal to the frequency.

In another feature, the computer program further comprises comparing thefirst and second counts to determine the frequency variation. Thecomputer program further comprises determining that the RF signal istone radar when the first and second counts are approximately equal.

In another feature, the computer program further comprises sampling theRF signals for a third predetermined period that is subsequent to thesecond predetermined period and incrementing a third count when thesamples collected during the third predetermined period reversepolarity.

In another feature, the computer program further comprises determining afirst difference between the first and second counts and a seconddifference between the second and third counts. The computer programfurther comprises determining a third difference between the first andsecond differences.

In another feature, the computer program further comprises determiningthe first and second differences when the first, second, and thirdcounts are greater than a predetermined threshold.

In another feature, the computer program further comprises determiningthat the RF signal is chirp radar when the third difference is less thana predetermined threshold. The predetermined threshold is approximatelyzero.

In another feature, the computer program further comprises determiningthat the RF signal is chirp radar when the third difference isapproximately zero.

In another feature, the computer program further comprises determiningwhether the RF signal is one of chirp radar and tone radar based on thefrequency variation. The computer program further comprises determiningthat the RF signal is chirp radar when the frequency variation islinear. The computer program further comprises determining that the RFsignal is tone radar when the frequency variation is approximately zero.

In another feature, the computer program further comprises selecting asecond channel having a different frequency than the first channel whenthe RF signal is one of chirp radar and tone radar.

In another feature, the computer program further comprises disregardingand excluding at least one of the samples from the first and secondcounts when an absolute value of the at least one of the samples is lessthan a predetermined threshold.

In another feature, the predetermined threshold is approximately 0.1.

In another feature, the first and second periods are adjacent.

In another feature, the first, second, and third periods are adjacent.

In still other features, the systems and methods described above areimplemented by a computer program executed by one or more processors.The computer program can reside on a computer readable medium such asbut not limited to memory, non-volatile data storage and/or othersuitable tangible storage mediums.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the disclosure, are intended forpurposes of illustration only and are not intended to limit the scope ofthe disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is functional block diagram of a wireless network operating in aninfrastructure mode according to the prior art;

FIG. 2 is a function block diagram of a wireless network operating in anad-hoc mode according to the prior art;

FIG. 3 a functional block diagram of an exemplary system for detectingradar and performing DFS in a wireless network according to the presentdisclosure;

FIG. 4 lists parameters of various exemplary short-pulse radar signalsthat may be used to detect radar and perform DFS;

FIG. 5A depicts an exemplary response of AGC gain to a chirp radar pulsefollowed by a wireless data packet;

FIG. 5B depicts exemplary samples of a chirp radar pulse and a wirelessdata packet received by an analog-to-digital converter (ADC) whenautomatic gain control (AGC) is off;

FIG. 6A depicts an exemplary response of AGC gain to a burst of threeradar pulses followed by a wireless data packet;

FIG. 6B depicts an exemplary decrease and increase in AGC gain inresponse to a radar pulse;

FIG. 7 depicts an exemplary method for measuring frequency of a radarpulse;

FIG. 8 is a graph depicting data samples of a baseband signal versustime;

FIG. 9 is an exemplary functional block diagram of a frequency module ofthe system depicted in FIG. 3;

FIG. 10 is an exemplary functional block diagram of a frequencycharacteristic module of the frequency module of FIG. 9;

FIG. 11 is graph of number of zero-crossings in a bin as a function ofnumber of bins when chirp radar pulses are centered at a centerfrequency of a frequency measuring device;

FIG. 12 is graph of number of zero-crossings in a bin as a function ofnumber of bins when chirp radar pulses are not centered at a centerfrequency of a frequency measuring device;

FIG. 13 is a flowchart depicted exemplary steps taken by the frequencymodule of FIG. 3;

FIG. 14 is a flowchart depicting exemplary steps taken by the frequencycharacteristic module of FIG. 9;

FIG. 15A is a functional block diagram of a high definition television;

FIG. 15B is a functional block diagram of a cellular phone;

FIG. 15C is a functional block diagram of a set top box; and

FIG. 15D is a functional block diagram of a media player.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is in no wayintended to limit the disclosure, its application, or uses. For purposesof clarity, the same reference numbers will be used in the drawings toidentify similar elements. As used herein, the term module, circuitand/or device refers to an Application Specific Integrated Circuit(ASIC), an electronic circuit, a processor (shared, dedicated, or group)and memory that execute one or more software or firmware programs, acombinational logic circuit, and/or other suitable components thatprovide the described functionality. As used herein, the phrase at leastone of A, B, and C should be construed to mean a logical (A or B or C),using a non-exclusive logical or. It should be understood that stepswithin a method may be executed in different order without altering theprinciples of the present disclosure.

Dynamic frequency selection (DFS) is typically used to avoidinterference between radar signals and wireless network communicationsystems operating in the 5 GHz band. More specifically, DFS is used toselect a radar-free channel for wireless network communication frommultiple non-overlapping channels in the 5.25-5.35 GHz and 5.47-5.725GHz frequency ranges.

Referring now to FIG. 3, a system 40 for radar detection and DFS mayinclude an automatic gain control (AGC) module 42, a radar module 44, aclear channel assessment (CCA) module 46, an analog-to-digital converter(ADC) module 48, a filter module 50, and a dynamic frequency selection(DFS) module 52.

The AGC module 42 provides a radio signal strength indicator (RSSI)measurement to the radar module 44. Based on RSSI, the radar module 44determines if a radio frequency (RF) signal is stronger than apredetermined threshold DFS_(th) such as −64 dBm. The CCA module 46distinguishes legitimate wireless data packets from other signals andactivates the radar module 44 when the RF signal is not a legitimatewireless data packet. The radar module 44 measures parameters of the RFsignal such as pulse width, frequency, frequency variation, etc. Morespecifically, the radar module 44 may include a frequency module 53 thatmeasures frequency and frequency variation of an RF signal. The DFSmodule 52 may compare the parameters measured by the radar module 44with a set of parameters of known types of radar signals. The system 40may switch to a different channel if the RF signal is a radar signal ofa known type.

The system 40 may be implemented in a wireless network device 54 such asan access point or a client station. The wireless network device 54typically includes an RF transceiver module 56, a baseband processor(BBP) module 58, and a medium access controller (MAC) module (or acontrol module) 60.

The RF transceiver 56 receives RF signals. The BBP module 58demodulates, digitizes, and filters the RF signal. The BBP module 58 mayinclude the AGC module 42, the ADC module 48, and the filter module 50.The control module 60 may include the radar module 44, the CCA module46, and the DFS module 52.

In some implementations, the radar module 44, the CCA module 46, and theDFS module 52 may be implemented in the BBP module 58 of the wirelessnetwork device 54. In still other implementations, at least one of themodules may be implemented by firmware and/or software. Although shownseparately for illustrative purposes, at least one of the modules shownin FIG. 3 may be implemented using a single module.

Additionally, the system 40 may be implemented in any other devicesand/or systems that may be used to detect radar. Although the disclosureexplains how the system 40 may be used to detect chirp radar, a skilledartisan may use the system 40 to detect and measure frequency variationsin signals other than radar.

Radar signals may be generally classified into three categories:short-pulse radar signals, long-pulse or chirp radar signals, andfrequency-hopping radar signals. A table in FIG. 4 lists sampleparameters for four exemplary short-pulse radar signals. In a chirpradar signal, the frequency of the carrier is linearly varied withinradar pulses. For example, a typical chirp radar signal may have a pulsewidth (PW) of 50-100 μS, a pulse repetition interval (PRI) of 1-2 mS,and a chirp width of 5-20 MHz. A typical frequency-hopping radar signalmay have a PW of 1 μS, a PRI of 333 μS, and 9 pulses per hop. Parametervalues of radar signals used in actual applications may vary.

Referring now to FIGS. 5A-6B, a response of AGC gain to different typesof radar signals is depicted. FIG. 5A depicts a response of AGC gain toa chirp radar pulse followed by a wireless data packet. FIG. 5B depictsexemplary samples of a chirp radar pulse 74 and a wireless data packet72 received by the ADC module 48 when the AGC is off. FIG. 5B alsodepicts a variation 73 in the signal input to the ADC module 48, whenthe AGC is off, corresponding to a varying frequency of chirp radar.FIG. 6A depicts a response of AGC gain to a burst of three radar pulsesfollowed by a wireless data packet. FIG. 6B depicts in detail a decrease78 and an increase 80 in AGC gain in response to a radar pulse.

When the RF transceiver 56 receives an RF signal, the gain of the AGCmodule 42 typically decreases to a value that is less than a normalvalue. The gain of the AGC module 42 may return to the normal valueafter a period of time. The time taken by the gain of the AGC module 42to return to the normal value depends on various parameters of the RFsignal such as signal strength, pulse width, frequency, etc. The AGCmodule 42 uses a radio signal strength indicator (RSSI) to communicatethe strength of the RF signal to the radar module 44. If RSSI exceeds athreshold value DFS_(th) such as −64 dBm, the radar module 44 mayperform radar detection.

The CCA module 46 may determine whether the RF signal is a legitimatewireless data packet. A preamble in a legitimate wireless data packetincludes a standard sequence. The CCA module 46 performs a correlationon the sequence in the preamble to determine whether the RF signal is alegitimate wireless data packet. The CCA module 46 uses a CCA signal toactivate the radar module 44 when the RF signal is not a legitimatewireless data packet. Thus, the CCA module 46 may prevent falsetriggering of the radar module 44. More specifically, the CCA module 46may prevent the radar module 44 from performing radar detection and DFSwhen the RF signal is a legitimate wireless data packet. In addition,the CCA module 46 may prevent the radar module 44 from being falselytriggered by Bluetooth jammers.

The ADC module 48 converts the RF signal from an analog to a digitalformat. When the RF signal is no longer being received, the output ofthe ADC decreases to a low value. The radar module 44 monitors theoutput of the ADC module 48. When the output of the ADC module 48decreases below a predetermined threshold and remains below thepredetermined threshold for a period of time, the radar module 44detects an ADC under-run condition. The ADC under-run conditionindicates an end of a pulse of the RF signal. The radar module 44determines characteristics of the RF signal such as pulse width (PW),frequency, frequency variation, etc., based on the ADC under-runcondition.

The filter module 50 typically includes a low-pass filter that filtersthe output of the ADC module 48. The radar module 44 determines whetherthe RF signal is single tone radar or chirp radar based on the output ofthe filter module 50. More specifically, the frequency module 53determines the frequency and frequency variation of the RF signal. Thefrequency module 53 determines characteristics of the RF signal based onthe frequency variation. The characteristics of the RF signal may beused to determine whether the RF signal is single tone radar or chirpradar.

The radar module 44 determines parameters of the RF signal such as pulsewidth, frequency, frequency characteristics (e.g., chirp frequency,single tone frequency, etc.), and pulse repetition interval (PRI). TheDFS module 52 compares the parameters determined by the radar module 44to the exemplary parameters shown in the table in FIG. 4 to determinewhether the RF signal is a radar signal of a known type.

When the signal strength of the RF signal exceeds DFS_(th) and when theCCA module 46 indicates that the RF signal is not a legitimate wirelessdata packet, the radar module 44 measures pulse width of every pulse ofthe RF. More specifically, the radar module 44 determines a beginning ofa pulse based on the RSSI signal generated by the AGC module 42. TheRSSI signal indicates a beginning of a pulse when the AGC gain crossesthe −64 dBm threshold. An end of a pulse is indicated by the ADCunder-run condition detected by the radar module 44 at the end of everypulse. The radar module 44 calculates the pulse width of the pulse bycounting a difference between the time of the beginning of the pulse andthe time of the end of the pulse.

Additionally, after receiving the ADC under-run signal at the end of thepulse, the radar module 44 generates a signal to reset the gain of theAGC module 42 to the normal value. Unless reset, the gain of the AGCmodule 42 may take longer to return to the normal value, and incomingdata during that time period may be lost.

Referring now to FIG. 7, the frequency module 53 measures the frequencyof the RF signal to determine characteristics of the signal. Aspreviously mention, the characteristics may be used to determine whetherthe RF signal is a single tone radar signal or a chirp radar signal. Thefrequency module 53 divides a baseband signal into bins of equalperiods. The period of each bin is proportional to the resolution of thefrequency measurement. In some implementations, the frequency module 53may determine the frequency of the RF signal when the gain of the AGCmodule 42 decreases below a predetermined threshold DFS_(th) (typically−64 dBm).

The frequency module 53 determines the frequency of the RF signal foreach bin. More specifically, the frequency module 53 countszero-crossings for each bin to determine the frequency. By counting thenumber of zero-crossings, the frequency module 53 may utilize lessresources than more complex methods that use Fourier transforms (e.g.,DFT, FFT).

Referring now to FIG. 8, a graph depicting data samples of the basebandsignal versus time is shown. Due to noise in the RF signal, the sampleddata may have multiple zero-crossings like those generally depicted at86 and 88. However, the baseband signal may have only two truezero-crossings as shown in FIG. 8. Therefore, the frequency module 53only counts zero-crossings of data samples that have an absolute value(ABS) greater than a predetermined ABS threshold. By counting datasamples that have an absolute value greater than the ABS threshold, thefrequency module 53 may count two zero-crossings rather than tenzero-crossings for the baseband signal shown in FIG. 8. In someimplementations, the ABS threshold may be 0.1, although other thresholdsmay be used.

Referring now to FIG. 9, an exemplary implementation of the frequencymodule 53 is depicted. The frequency module 53 may include a samplingmodule 100, an ABS module 102, a polarity comparator 104, a counter 106,a timer 108, a clock 110, memory 112, and a frequency characteristicmodule 114.

The sampling module 100 may communicate with the ADC module 48, the ABSmodule 102, and the timer 108. The polarity comparator 104 maycommunicate with the ABS module 102, the counter 106, and memory 112.The counter 106 may communicate with the timer 108 and memory 112. Theclock 110 may communicate with the timer 108.

The clock 110 may periodically set the timer 108 to count down from apredetermined time. The predetermined time may correspond with theperiod of the bin. While the timer 108 is counting down, the samplingmodule 100 may collect data samples from the ADC module 48. The ABSmodule 102 may receive the samples from the sampling module 100 anddiscard samples that have an absolute value less than the ABS threshold.The polarity comparator 104 compares the remaining samples to a previoussample stored in memory 112. If the polarity of the previous sample isopposite of the sample, a zero-crossing has occurred. When azero-crossing occurs, the polarity comparator 104 directs the counter106 to increment a count total and stores the sample in memory 112. Thecounter 106 stores the count total in memory 112 when the timer 108expires. The count total sampled during the predetermined time generallycorresponds to the frequency of the RF signal for each bin.

The frequency characteristic module 114 may communicate with memory 112and determine frequency characteristics of the count totals (orfrequencies) stored in memory 112. More specifically, the frequencycharacteristic module 114 compares the frequencies of each bin anddetermines whether the frequencies vary according to a predeterminedpattern. For example, if the frequencies vary according to a linearpattern, the RF signal may be chirp radar. If the frequencies aresubstantially the same from bin to bin, the RF signal may be tone radar.

Referring now to FIG. 10, an exemplary implementation of the frequencycharacteristic module 114 is depicted. The frequency characteristicmodule 114 may include a tone module 150 and a chirp module 152. Thetone module 114 may determine whether the RF signal is tone radar, andthe chirp module 152 may determine whether the RF signal is chirp radar.Although this example only includes the tone and chirp modules 150, 152,other modules may be included to determine other frequency variationcharacteristics of the RF signal.

The tone module 150 may include a tone comparator 154. The tonecomparator 154 may compare the frequencies of each bin stored in memory112. If the frequencies are substantially the same, the tone module 150may determine the RF signal to be tone. To determine whether thefrequencies are substantially the same, the tone comparator 154 may alsocompare the variation of each bin to a tone threshold.

The chirp module 152 determines whether the frequency of the RF signalvaries linearly, in which case the RF signal may be chirp radar. FIG. 11depicts evenly distributed zero-crossings where pulses of chirp radarare centered at a center frequency of a DFS-enabled device receiving thechirp radar signal. Chirp radar may include a down-chirp as generallydepicted at 180 and an up-chirp as generally depicted at 182. Since thedown-chirp and up-chirp are linear in nature, the chirp module 152 maydetermine that the RF signal is chirp radar when the pattern is linear.

FIG. 12 depicts unevenly distributed zero crossings where pulses ofchirp radar are not centered at the center frequency of the DFS-enableddevice receiving the radar signal. As with FIG. 11, chirp radar that isnot centered at the center frequency is also linear in nature.Down-chirps of the RF signal are generally depicted at 184 and up-chirpsare generally depicted at 186.

Referring back to FIG. 10, the chirp module 152 may include a high passmodule 156, a chirp comparator 158, and a derivative module 160. Binsthat have a low frequency may be sensitive to random noise and areexcluded when determining the frequency characteristics. Therefore, thehigh pass module 156 may be used to remove bins with a frequency lessthan a frequency threshold from consideration when determining thefrequency variation.

The derivative module 160 may approximate a first and second derivativeof the frequencies of each bin stored in memory 112. The secondderivative may be used to determine whether the frequency variation islinear. More specifically, if the second derivative is approximatelyzero, the frequency variation is linear. If the frequency variation islinear, the chirp module 152 may determine that the RF signal is chirpradar due to the linear characteristics of chirp radar.

To determine the first and second derivatives of the frequencies, thederivative module 160 may use difference equations. The first derivativemay be determined with the following equation:d _(i) =|z _(i) −z _(i+1)|where d_(i) is the first derivative, z_(i) is the frequency in a currentbin, and z_(i+1) is the frequency in the next bin. The second derivativemay be determined with the following equation:s=|d _(i) −d _(i+1)|where s is the second derivative, d_(i) is the first derivative of thefrequency in a current bin, and d_(i+1) is the first derivative of thefrequency in the next bin.

The chirp comparator 158 determines whether the second derivative isapproximately zero. More specifically, the chirp comparator 158 maycompare the second derivative of the frequencies to a chirp thresholdthat is slightly greater than zero. If the second derivative is lessthan the chirp threshold, then the second derivative is approximatelyzero. If the second derivative is approximately zero, the chirp module150 may determine RF signal to be chirp radar.

Referring now to FIG. 13, exemplary steps taken by the frequency module53 to determine the frequency of the RF signal are generally depicted at200. The process starts in step 202 when the RF transceiver 56 receivesthe RF signal. In step 203, the clock 110 sets the timer 108 tocountdown from a predetermined time. In step 204, the counter 106 isinitialized to zero. The sampling module 100 collects data samples fromthe ADC module 48 in step 206.

In step 208, the ABS module 102 determines an absolute value of thesamples. The ABS module 102 determines whether the absolute value of thesample is greater than the ABS threshold in step 210. If the absolutevalue of the sample is greater than the ABS threshold, the polaritycomparator 104 determines whether the polarity of the sample hastransitioned in step 212. If the polarity of the sample hastransitioned, the counter 106 increments in step 214. In step 216, thefrequency module 53 determines whether the timer 108 has expired. If thetimer 108 has expired, the value that the counter 106 has incremented tois stored in memory 112 in step 218 and the process ends in step 220. Ifthe timer 108 has not expired, the process returns to step 206.

If the ABS module 102 determines that the absolute value of the sampleis not greater than the ABS threshold in step 210, the ABS module 102discards the sample in step 222. The frequency module 53 determineswhether the timer 108 has expired in step 216. If the timer 108 hasexpired, the value that the counter 106 has incremented to is stored inmemory 112 in step 218 and the process ends in step 220. If the timer108 has not expired, the process returns to step 206.

If the polarity comparator 104 determines that the polarity of thesample has not transitioned in step 212, the frequency module 53determines whether the timer 108 has expired in step 216. If the timer108 has expired, the value that the counter 106 has incremented to isstored in memory 112 in step 218 and the process ends in step 220. Ifthe timer 108 has not expired, the process returns to step 206.

Referring now to FIG. 14, exemplary steps taken by the frequencycharacteristic module 114 to determine whether the frequencies stored inmemory vary according to a particular pattern are generally depicted at250. The process begins in step 252. In step 253, the frequencycharacteristic module 114 reads the frequency of a bin from memory 122.In step 254, the tone comparator 154 determines whether the frequenciesare substantially the same from bin to bin. More specifically, the tonecomparator 154 compares the frequency read from memory 122 to afrequency that was previously read from memory. If the frequencies frombin to bin are substantially the same, the tone module 150 may determinethat the RF signal is tone radar in step 256 and the process ends instep 258.

If the tone comparator 154 determines that the frequencies are notsubstantially the same from bin to bin in step 254, the frequencycomparator 156 determines whether the frequency is greater than afrequency threshold in step 260. If the frequency is not greater thanthe frequency threshold, the frequency characteristic module 114determines whether there are more bins in memory 112 in step 262. Ifthere are more bins in memory 112, the frequency module 114 reads thefrequency of the next bin stored in memory 112 in step 253.

If the frequency comparator 156 determines that the frequency is greaterthan the frequency threshold, the derivative module 160 determines thefirst derivative in step 264 and the second derivative in step 266. Instep 268, the chirp comparator 158 determines whether the secondderivative is less than the chirp threshold. If the second derivative isless than the chirp threshold, the chirp module 152 determines that theRF signal is chirp radar in step 270 and the process ends in step 258.If the second derivative is not less than the chirp threshold, theprocess ends in step 258.

Referring now to FIGS. 15A-15D, various exemplary implementations of thesystem 40 are shown. Referring now to FIG. 15A, the system 40 can beimplemented in signal processing and/or control circuits 422 of a highdefinition television (HDTV) 420. The HDTV 420 receives HDTV inputsignals in either a wired or wireless format and generates HDTV outputsignals for a display 426. In some implementations, signal processingcircuit and/or control circuit 422 and/or other circuits (not shown) ofthe HDTV 420 may process data, perform coding and/or encryption, performcalculations, format data and/or perform any other type of HDTVprocessing that may be required.

The HDTV 420 may communicate with mass data storage 427 that stores datain a nonvolatile manner in devices such as optical and/or magneticstorage devices. The devices may include, for example, hard disk drivesHDD and/or DVDs. The HDD may be a mini HDD that includes one or moreplatters having a diameter that is smaller than approximately 1.8″. TheHDTV 420 may be connected to memory 428 such as RAM, ROM, low latencynonvolatile memory such as flash memory and/or other suitable electronicdata storage. The HDTV 420 also may support connections with a WLAN viaa WLAN network interface 429.

Referring now to FIG. 15B, the system 40 can be implemented in signalprocessing and/or control circuits 452 of a cellular phone 450 that mayinclude a cellular antenna 451. In some implementations, the cellularphone 450 includes a microphone 456, an audio output 458 such as aspeaker and/or audio output jack, a display 460 and/or an input device462 such as a keypad, pointing device, voice actuation and/or otherinput device. The signal processing and/or control circuits 452 and/orother circuits (not shown) in the cellular phone 450 may process data,perform coding and/or encryption, perform calculations, format dataand/or perform other cellular phone functions.

The cellular phone 450 may communicate with mass data storage 464 thatstores data in a nonvolatile manner in devices such as optical and/ormagnetic storage devices. The devices may include, for example, harddisk drives HDD and/or DVDs. The HDD may be a mini HDD that includes oneor more platters having a diameter that is smaller than approximately1.8″. The cellular phone 450 may be connected to memory 466 such as RAM,ROM, low latency nonvolatile memory such as flash memory and/or othersuitable electronic data storage. The cellular phone 450 also maysupport connections with a WLAN via a WLAN network interface 468.

Referring now to FIG. 15C, the system 40 can be implemented in signalprocessing and/or control circuits 484 of a set top box 480. The set topbox 480 receives signals from a source such as a broadband source andoutputs standard and/or high definition audio/video signals suitable fora display 488 such as a television and/or monitor and/or other videoand/or audio output devices. The signal processing and/or controlcircuits 484 and/or other circuits (not shown) of the set top box 480may process data, perform coding and/or encryption, performcalculations, format data and/or perform any other set top box function.

The set top box 480 may communicate with mass data storage 490 thatstores data in a nonvolatile manner. The mass data storage 490 mayinclude optical and/or magnetic storage devices such as hard disk drivesHDD and/or DVDs. The HDD may be a mini HDD that includes one or moreplatters having a diameter that is smaller than approximately 1.8″. Theset top box 480 may be connected to memory 494 such as RAM, ROM, lowlatency nonvolatile memory such as flash memory and/or other suitableelectronic data storage. The set top box 480 also may supportconnections with a WLAN via a WLAN network interface 496.

Referring now to FIG. 15D, the system 40 can be implemented in signalprocessing and/or control circuits 504 of a media player 500. In someimplementations, the media player 500 includes a display 507 and/or auser input 508 such as a keypad, touchpad and the like. In someimplementations, the media player 500 may employ a graphical userinterface (GUI) that typically employs menus, drop down menus, iconsand/or a point-and-click interface via the display 507 and/or user input508. The media player 500 further includes an audio output 509 such as aspeaker and/or audio output jack. The signal processing and/or controlcircuits 504 and/or other circuits (not shown) of the media player 500may process data, perform coding and/or encryption, performcalculations, format data and/or perform any other media playerfunction.

The media player 500 may communicate with mass data storage 510 thatstores data such as compressed audio and/or video content in anonvolatile manner. In some implementations, the compressed audio filesinclude files that are compliant with MP3 format or other suitablecompressed audio and/or video formats. The mass data storage may includeoptical and/or magnetic storage devices such as hard disk drives HDDand/or DVDs. The HDD may be a mini HDD that includes one or moreplatters having a diameter that is smaller than approximately 1.8″. Themedia player 500 may be connected to memory 514 such as RAM, ROM, lowlatency nonvolatile memory such as flash memory and/or other suitableelectronic data storage. The media player 500 also may supportconnections with a WLAN via a WLAN network interface 516. Still otherimplementations in addition to those described above are contemplated.

Those skilled in the art can now appreciate from the foregoingdescription that the broad teachings of the disclosure can beimplemented in a variety of forms. Therefore, while this disclosureincludes particular examples, the true scope of the disclosure shouldnot be so limited since other modifications will become apparent to theskilled practitioner upon a study of the drawings, the specification andthe following claims.

What is claimed is:
 1. A system comprising: a counting module configuredto count polarity reversals of samples of a signal, wherein the samplesare generated during (i) a first period, (ii) a second period, and (iii)a third period, and generate (i) a first count, (ii) a second count, and(iii) a third count of the polarity reversals counted during therespective periods; a difference module configured to determine a firstdifference between (i) the first count and (ii) the second count, asecond difference between (i) the second count and (ii) the third count,and a third difference between (i) the first difference and (ii) thesecond difference; and a radar module configured to determine variationin frequency of the signal based on (i) the first count and (ii) thesecond count, and determine a type of radar present in the signal basedon one or more of (i) the third difference and (ii) the variation in thefrequency of the signal.
 2. The system of claim 1, wherein the radarmodule is configured to determine that the type of radar present in thesignal is chirp radar in response to the third difference being lessthan a predetermined threshold.
 3. The system of claim 1, wherein theradar module is configured to determine that the type of radar presentin the signal is tone radar in response to the variation in thefrequency of the signal being less than a predetermined value.
 4. Thesystem of claim 2, wherein: the predetermined threshold includes a firstpredetermined threshold, and the difference module is configured todetermine the first difference and the second difference in response tothe first count, the second count, and the third count being greaterthan a second predetermined threshold.
 5. The system of claim 2, whereinthe predetermined threshold is zero.
 6. The system of claim 1, whereinthe radar module is configured to determine that the type of radarpresent in the signal is chirp radar in response to the third differencebeing zero.
 7. The system of claim 1, wherein the radar module isconfigured to determine that the type of radar present in the signal ischirp radar or tone radar based on the variation in the frequency of thesignal.
 8. The system of claim 7, wherein the radar module is configuredto determine that the type of radar present in the signal is chirp radarin response to the variation in the frequency of the signal beinglinear.
 9. The system of claim 7, wherein the radar module is configuredto determine that the type of radar present in the signal is tone radarin response to the variation in the frequency of the signal being zero.10. The system of claim 1, wherein the difference module is configuredto exclude one or more of the samples from one or more of (i) the firstcount and (ii) the second count in response to an absolute value of theone or more of the samples being less than a predetermined threshold.11. A wireless network device comprising: the system of claim 1, whereinthe wireless network device is configured to receive the signal whilecommunicating in a first channel; and a dynamic frequency selectionmodule configured to switch to a second channel in response to the radarmodule determining that radar is present in the signal.
 12. A methodcomprising: counting polarity reversals of samples of a signal receivedby a wireless network device, wherein the samples are generated during(i) a first period, (ii) a second period, and (iii) a third period; andgenerating (i) a first count, (ii) a second count, and (iii) a thirdcount of the polarity reversals counted during the respective periods;generating a first difference between (i) the first count and (ii) thesecond count; generating a second difference between (i) the secondcount and (ii) the third count; generating a third difference between(i) the first difference and (ii) the second difference; determining afrequency of the signal based on one or more of (i) the first count and(ii) the second count; determining variation in the frequency of thesignal based on (i) the first count and (ii) the second count; anddetermining (a) whether radar is present in the signal, and in responseto radar being present in the signal, (b) a type of radar present in thesignal received by the wireless network device based on one or more of(i) the third difference and (ii) the variation in the frequency of thesignal.
 13. The method of claim 12, further comprising determining thatthe type of radar present in the signal is chirp radar in response tothe third difference being less than a predetermined threshold.
 14. Themethod of claim 12, further comprising determining that the type ofradar present in the signal is tone radar in response to the variationin the frequency of the signal being less than a predetermined value.15. The method of claim 13, wherein the predetermined threshold includesa first predetermined threshold, the method further comprising:determining the first difference and the second difference in responseto the first count, the second count, and the third count being greaterthan a second predetermined threshold.
 16. The method of claim 13,wherein the predetermined threshold is zero.
 17. The method of claim 12,further comprising determining that the type of radar present in thesignal is chirp radar in response to the third difference being zero.18. The method of claim 12, further comprising determining that the typeof radar present in the signal is chirp radar or tone radar based on thevariation in the frequency of the signal.
 19. The method of claim 18,further comprising determining that the type of radar present in thesignal is chirp radar in response to the variation in the frequency ofthe signal being linear.
 20. The method of claim 18, further comprisingdetermining that the type of radar present in the signal is tone radarin response to the variation in the frequency of the signal being zero.21. The method of claim 12, further comprising excluding one or more ofthe samples from one or more of (i) the first count and (ii) the secondcount in response to an absolute value of the one or more of the samplesbeing less than a predetermined threshold.
 22. The method of claim 12,wherein the wireless network device is configured to receive the signalwhile communicating in a first channel, the method further comprising:switching to a second channel in response to determining that radar ispresent in the signal.